1. Field of the Invention
The present invention relates to a discharge lamp lighting device having a starting circuit unit that integrally includes a socket on which a discharge lamp is mounted and a starting circuit for starting the discharge lamp.
2. Description of the Related Art
Recently, a discharge lamp (HID lamp) has been used as a light source of a headlamp for a motor vehicle use. For example, JP 2001-102142 A discloses, as a discharge lamp lighting device for lighting such a discharge lamp, a discharge lamp lighting device having a starting circuit unit in which a socket on which a discharge lamp is mounted and a starting circuit for starting the discharge lamp are integrally provided, and all internal constituent components in the unit are covered with an external wall.
The starting circuit of the discharge lamp lighting device has a high voltage transformer generating a high-voltage pulse necessary to start its discharge lamp. Such a high voltage transformer calls for covering itself with a member such as a container or a barrier plate aimed insulating its high voltage portion. For this reason, a high voltage transformer is previously configured as a component that has no exposed high voltage portion, and then the transformer generating high voltage is covered along with other circuits with a cover which is separately fabricated beforehand, thereby uniting a discharge lamp lighting device as a socket for connecting a discharge lamp having a built-in starting circuit.
Meanwhile, in a discharge lighting device for a vehicle, the higher the function of a vehicle, the larger the number of components mounted in an engine room is. As a result, in a recent discharge lamp lighting device for a vehicle use, a space around a headlamp tends to be narrowed. Therefore, there is great need for size reduction of a discharge lamp lighting device. Particularly, it shows a marked trend toward a discharge lamp lighting device having a starting circuit unit in which a socket and a starting circuit are integrally provided because of an extremely large size of the unit placed at the back of the discharge lamp.
In order to achieve such size reduction with the existing discharge lamp lighting device, it has no other choice but to thin thickness of the cover out of a double-layered wall, i.e., a barrier plate for insulating the transformer generating high voltage and the cover constituting an external wall of the starting circuit unit. However, to use as a cover, thinning the thickness of the cover to excess is absolutely nonsense for lack of its stiffness, and one strikes against technical bounds in fabricating a thin cover from the beginning. Therefore, there has been unsurmountable bounds as far as one takes the foregoing conventional structure.